Re: [PATCH 0/8] DPF (GPU l3 parity detection) improvements

Bell, Bryan J
2013-09-17T00:52:25Z

The "hang" injection is for the scenarios like:
(1) L3 error occurs
(2) Workload completion, reported to user mode driver, e.g. OpenCL
(3) L3 error interrupt, handled.

If (2) occurs before (3), it's possible to report that a GPGPU workload successfully completed when in fact it did not due to the L3 error.

It should be up to the user mode if the "hang" bit is set.

--Thanks
Bryan
-----Original Message-----
From: Ben Widawsky [mailto:benjamin.widawsky@intel.com]
Sent: Thursday, September 12, 2013 10:28 PM
To: intel-gfx@lists.freedesktop.org
Cc: Venkatesh, Vishnu; Bell, Bryan J; Widawsky, Benjamin
Subject: [PATCH 0/8] DPF (GPU l3 parity detection) improvements

Since IVB, our driver has supported GPU L3 cacheline remapping for parity errors. This is known as, "DPF" for Dynamic Parity Feature. I am told such an error is a good predictor for a subsequent error in the same part of the cache. To address this possible issue for workloads requiring precise and correct data, like GPGPU workloads the HW has extra space in the cache which can be dynamically remapped to fill in the old, faulting parts of the cache. I should also note, to my knowledge, no such error has actually been seen on either Ivybridge or Haswell in the wild.

Note, and reminder: GPU L3 is not the same thing as "L3." It is a special (usually incoherent) cache that is only used by certain components within the GPU.

Included in the patches:
1. Fix HSW test cases previously submitted and bikeshedded by Ville.
2. Support for an extra area of L3 added in certain HSW SKUs 3. Error injection support from the user space for test.
4. A reference daemon for listening to the parity error events.

Caveats:
* I've not implemented the "hang" injection. I was not clear what it does, and
I don't really see how it benefits testing the software I have written.

* I am currently missing a test which uses the error injection.
Volunteers who want to help, please raise your hand. If not, I'll get
to it as soon as possible.

* We do have a race with the udev mechanism of error delivery. If I
understand the way udev works, if we have more than 1 event before the
daemon is woken, the properties will get us the failing cache location
of the last error only. I think this is okay because of the earlier statement
that a parity error is a good indicator of a future parity error. One thing
which I've not done is trying to track when there are missed errors which
should be possible even if the info about the location of the error can't be
retrieved.

* There is no way to read out the per context remapping information through
sysfs. I only expose whether or not a context has outstanding remaps through
debugfs. This does effect the testability a bit, but the implementation is
simple enough that I'm not terrible worried.

Ben Widawsky (8):
drm/i915: Remove extra "ring"
drm/i915: Round l3 parity reads down
drm/i915: Fix l3 parity user buffer offset
drm/i915: Fix HSW parity test
drm/i915: Add second slice l3 remapping
drm/i915: Make l3 remapping use the ring
drm/i915: Keep a list of all contexts
drm/i915: Do remaps for all contexts

drivers/gpu/drm/i915/i915_debugfs.c | 23 ++++++---
drivers/gpu/drm/i915/i915_drv.h | 13 +++--
drivers/gpu/drm/i915/i915_gem.c | 46 +++++++++---------
drivers/gpu/drm/i915/i915_gem_context.c | 20 +++++++-
drivers/gpu/drm/i915/i915_irq.c | 84 +++++++++++++++++++++------------
drivers/gpu/drm/i915/i915_reg.h | 6 +++
drivers/gpu/drm/i915/i915_sysfs.c | 57 +++++++++++++++-------
drivers/gpu/drm/i915/intel_ringbuffer.c | 6 +--
include/uapi/drm/i915_drm.h | 8 ++--
9 files changed, 175 insertions(+), 88 deletions(-)

--
1.8.4